1. Field of the Invention
This invention relates to a light source for emitting light of a long wavelength for use in stage lighting, an auxiliary lamp of a vehicle or the like, and more particularly to a light source which is improved in luminous efficacy or lightening efficiency.
2. Description of the Prior Art
A fog lamp is provided as one of auxiliary lamps for an automobile. The fog lamp is lightened to emit light far in the distance at the occurrence of fog which absorbs and disturbs headlights so as to ensure safety driving.
The fog lamp emits light of a long wavelength exhibiting a luminous color of yellowish green or yellow in order to prevent light from being absorbed in fog or the like. For this purpose, the fog lamp generally employs a combination of a tungsten lamp and a filter to cut light of a short wavelength emitted from the lamp and obtain light of, for example, yellow luminous color.
In FIG. 9, the curve (a) shows a spectral distribution of a tungsten halogen lamp which is generally called a halogen lamp. When the halogen lamp is combined with a filter having spectral transmittance characteristics as indicated at the curve (b) in FIG. 9 light of yellow to red luminous color is obtained. This concept has been utilized in various kinds of lamps, such as, for example, a road lamp, a directional indication lamp, a stop lamp and a tail lamp for an automobile, a stage lighting lamp, and the like.
When a filter is used to obtain light of desired luminous color, light of a wavelength deviated from the transmission region of the filter is cut as exemplified by the halogen lamp shown in FIG. 9. In FIG. 9, the curve (b) indicates transmission characteristics of a filter combined with a halogen lamp light in a zone A indicated at oblique lines in FIG. 9 is absorbed in the filter and converted into useless heat within the filter, and energy in the zone (A) is wasted in vain.